1. Field of the Invention
This invention relates to deactivation of metal contaminants in catalytic cracking of hydrocarbons using an ultra large pore crystalline material and a metal passivator incorporated in the material.
2. Description of the Prior Art
Conversion of heavy petroleum fractions to lighter products by catalytic cracking is well known in the refining industry. Fluidized Catalytic Cracking (FCC) is particularly advantageous for that purpose. The heavy feed contacts hot regenerated catalyst and is cracked to lighter products. Carbonaceous deposits form on the catalyst, thereby deactivating it. The deactivated (spent) catalyst is separated from cracked products, stripped of strippable hydrocarbons and charged to a regenerator, where coke is burned off the catalyst with air, thereby regenerating the catalyst. The regenerated catalyst is then recycled to the reactor. The reactor-regenerator assembly are usually maintained in heat balance. Heat generated by burning the coke in the regenerator provides sufficient thermal energy for catalytic cracking in the reactor. Control of reactor conversion is usually achieved by controlling the flow of hot regenerated catalyst to the reactor to maintain the desired reactor temperature.
In most modern FCC units, hot regenerated catalyst is added to the feed at the base of a rise reactor. The fluidization of the solid catalyst particles may be promoted with a lift gas. Mixing and atomization of the feedstock may be promoted with steam, equal to 1-5 wt % of the hydrocarbon feed. Hot catalyst (above 650.degree. C.) from the regenerator is mixed with preheated (150.degree.-375.degree. C.) charge stock. The catalyst vaporizes and superheats the feed to the desired cracking temperature usually 450.degree.-600.degree. C. During the upward passage of the catalyst and feed, the feed is cracked, and coke deposits on the catalyst. The coked catalyst and the cracked products exit the riser and enter a solid-gas separation system, e.g., a series of cyclones, at the top of the reactor vessel. The cracked products are fractionated into a series of products, including gas, gasoline, light gas oil, and heavy cycle gas oil. Some heavy cycle gas oil may be recycled to the reactor. The bottoms product, a "slurry oil", is conventionally allowed to settle. The catalyst-rich solids portion of the settled product may be recycled to the reactor. The clarified slurry oil is a heavy product.
The "reactor vessel" into which the riser discharges primarily separates catalyst from cracked products and unreacted hydrocarbons and permits catalyst stripping.
Older FCC units use some or all dense bed cracking. Down flow operation is also possible, in which case catalyst and oil are added to the top of a vertical tube, or "downer", with cracked products removed from the bottom of the downer. Moving bed analogs of the FCC process, such as Thermofor Catalytic Cracking (TCC) are also known.
Further details on FCC can be found in U.S. Pat. No. 3,152,065 (Sharp et al); U.S. Pat. No. 3,261,776 (Banman et al); U.S. Pat. No. 3,654,140 (Griffel et al.); U.S. Pat. No. 3,812,029 (Snyder); U.S. Pat. Nos. 4,093,537, 4,118,337, 4,118,338, 4,218,306 (Gross et al); U.S. Pat. No. 4,444,722 (Owen); U.S. Pat. No. 4,459,203 (Beech et al.); U.S. Pat. No. 4,639,308 (Lee); U.S. Pat Nos. 4,675,099, 4,681,743 (Skraba) as well as in Venuto et al, Fluid Catalytic Cracking With Zeolite Catalysts, Marcel Dekker, Inc. (1979). These patents and publication are incorporated herein by reference.
Conventional FCC catalysts usually contain finely divided acidic zeolites comprising e.g., faujasites, such as Rare Earth Y (REY), Dealuminized Y (DAY), Ultrastable Y (USY), Rare Earth Ultrastable Y (RE-USY), silicon enriched dealuminized Y and Ultrahydrophobic Y (UBP-Y).
Typically, FCC catalysts are fine particles having particle diameters ranging from about 20 to 150 microns and an average diameter around 60-80 microns.
Catalyst for use in moving bed catalytic cracking units (e.g., TCC units) can be in the form of spheres, pills, beads, or extrudates, and can have a diameter ranging from 1 to 6 mm.
A process for catalytic cracking over an ultra large pore crystalline material catalyst has been described in U.S. Pat. No. 5,258,114. U.S. Pat. No. 5,258,114 describes a process particularly suited to converting "bottom of the barrel" or resid fractions into lighter components via catalytic cracking.
Although many advances have been made in catalytic cracking, and in cracking catalysts, some problem areas remain.
Heavy feeds available for processing, such as vacuum residua, contain contaminating metals which can include nickel, vanadium, iron, copper and molybdenum. These metals may be present in the hydrocarbon feed as free metals or as components of inorganic and organic compounds such as porphyrins and asphaltenes. Deposition of contaminating metals on cracking catalysts causes a gradual deterioration of the catalyst and unwanted side reactions, for example, producing hydrogen, light gases such as methane and ethane, and coke, at the expense of more valuable products.
Various methods have been described for trapping or passivating contaminating metals. In U.S. Pat. No. 5,258,114, metal getters or sinks such as alkaline and/or rare earth compounds may be present as part of the matrix or as separate additives of the metal getter alone.
In U.S. Pat. No. 4,921,824, discrete particles of lanthanum oxide or other rare earth oxides are added to the catalyst and hydrocarbon to passivate metal contaminants during catalytic cracking.
Problems caused by metal contaminants still remain.